The present invention relates to an optical scanning system to scan a code on an object comprising a laser source, a laser beam shaper receiving a laser beam from the laser source and focussing the laser beam on the object, a mirror polygon having at least two facets, of which at least one is reflective, and being rotated by a motor, a mirror array surrounding the polygon over at least half a circle and arranged in such a way that the laser beam after being reflected by the rotating polygon and by the mirrors of the mirror array will generate a scanning pattern on the code to be detected, and a detector receiving the light scatterred by the object.
Such an optical scanning device may be used as a bar code reader and is known from EP-A-0.375.340. The known device comprises a laser tube generating a laser beam, a beam shaper, at least one reflecting mirror that directs the laser beam to a polygon rotated by a motor and a mirror array of, for instance, three mirrors. The laser beam reflected from the rotary polygon is directed to the mirror array generating one scanning line per mirror on the bar code to be read. Every scanning line has its own direction. The polygon has, for instance, five facets. So, every turn of the entire polygon corresponds with five groups of three scanning lines. Depending on the angle of inclination of the polygon facets these groups might be in different planes. In the arrangement of EP-A-0.375.340 the mirror array can only be set up in at most half a circle around the polygon, thus limiting the maximum number of mirrors to be installed in the mirror array, and therefore limiting the number of scanning lines to be generated on the bar code.
DE-A-3.602.008 shows a bar code reading device comprising a polygon mirror, some facets of which might be flat, concave or convex. To every facet corresponds a separate plane in which a laser beam being reflected by this facet and afterwards focussed by a hollow, focussing mirror, is entirely focussed. Therefore, the depth of field in which a bar code can be read is increased. However, no use is made of a mirror array. So, no scanning lines with different orientations are generated, thereby limiting the number of possible orientations of the bar code to be read.
U.S. Pat. No. 4,450,350 shows a bar code reading device comprising at least one rotating polygon and a mirror array. One of the objects of this patent is to generate a multi-line scanning pattern on a bar code, in which the scanning speed is more than twice the rotating speed of the polygon. The mirrors of the mirror array are installed in at most half a circle around the polygon, thereby limiting the number of possible orientations of the scanning lines of the scanning pattern.